It is known art (DE-PS 1 116 973; Deutsche Offenlegungsschrift 27 47 093) to make the guide vanes of a prerotational swirl controller for rotary pumps variable in order to match the pump to different operating conditions. For this purpose, each guide vane is cantilevered from a trunnion which is led, in a sealed manner, through the casing of the flow duct containing the guide vanes, is rigidly supported in a bearing located outside the casing and is connected to an adjusting device. This arrangement has the disadvantage that the vanes are susceptible to vibration so that the bearings, trunnions and seals have to be very strongly dimensioned and that large adjustment forces occur. The bearings must be rigid and must be accurately connected to the casing in the radial direction. This can be avoided if, in addition to being supported at their outer ends on the casing, the guide vanes are supported at their ends near the center on a stationary hub located in the center of the duct, the hub carrying the bearing devices for the ends of the guide vanes (GB-A-671607; GB-A146452; DE-A-2447891). In practice, however, guide vanes supported at both ends are seldom found because this arrangement still further increases the already existing problems with respect to the assembly, dismantling and maintenance of the guide vanes. In known pumps, in fact, it is generally necessary to dismantle the casing in order to obtain access to the guide vanes and replace them. Although it is known art (GB-A-2201732) to provide, in the casing of a gas turbine, an assembly opening--which can be closed by means of a cap--on the periphery of the compressor rotor so that the compressor blades fastened to the shaft can be individually removed when they are located in a suitable angular position, different preconditions exist in that case compared with the present invention because only one assembly opening is necessary for all the blades and the latter are moreover not located on the casing and are not adjustable.
The object of the invention is based on the creation of a pre-rotational swirl controller for rotary pumps with limited bearing requirements, permits easy assembly and dismantling of the guide vanes. The object is achieved by providing a pre-rotational swirl controller for rotary pumps. The pre-rotational swirl controller has a flow duct enclosed by a casing and a plurality of guide cans located substantially within the casing, each guide vane being supported on the casing at one end and on a permanently located hub at the other end. The controller includes an adjusting device for the guide vanes, and a bearing located on a cap piece or closure which closes an opening in the casing appropriate to the cross-sectional side of the guide vanes. The bearing is designed to be tolerant of alignment errors.
Because the guide vanes are supported at both ends, the casing-end guide vane bearing does not need to accept large forces nor does it need to be specially aligned. This opens the possibility of locating it on the cap piece or closure which closes an opening in the outside of the casing appropriate to the cross-sectional size of the guide vane. This in turn creates the possibility of removing and fitting the guide vane through the casing for maintenance purposes. On the other hand, the arrangement of the bearing on the cap also increases the alignment error possibilities, which are neutralized because at least the bearing provided on the casing for the guide vane trunnions (possibly including the associated seals) is designed to be tolerant of alignment errors. The accuracy requirements in the manufacture and fitting of the bearing and cap are substantially reduced by this means.
Alignment error tolerance is less critical on the hub-end bearing of the guide vanes because, on the one hand, the tolerances caused by the cap design involve practically no alignment errors and, on the other hand, the hub-end bearing can generally be designed to be short and simple and therefore less sensitive to alignment errors.
As known per se (U.S. Pat. No. 2,606,713), the adjusting device can include a rolling-contact supported ring for the common adjustment of the guide vanes. In the case of liquid pumps, such a measure has not previously been employed because it cannot introduce any substantial improvement due to high frictional forces occurring at the bearings and seals. On the other hand, the adjustment forces are further reduced in association with the invention in which the bearing and sealing forces are smaller.
In accordance with a particular feature of the invention, a setting gear with a through drive shaft is used in the adjusting device. This has the advantage that when several swirl controllers are arranged in series (for example for the different stages of a pump arrangement), a through drive shaft can be employed. This has a particularly close relationship to the features of the invention previously mentioned because it is only due to these that the adjusting forces are so reduced that the drive shaft can be designed to be so thin that a through arrangement is advantageous and an extremely small drive motor is necessary. This feature possibly also deserves protection independent of the previously mentioned features, however, particularly in association with the further feature of the invention that the adjusting device includes a self-locking setting gear with a large transmission ratio. It is not only the large transmission ratio that contributes to the reduction of the drive forces, and hence to the dimensions of the drive shaft; the self-locking property of the setting gear also contributes because no retention forces have to be accepted by the drive shaft. A gear of the sliding wedge type is particularly advantageous.
The invention is explained in more detail below with reference to the drawing which shows an advantageous illustrative example.